Photo-electric system



Patented Feb. 24, 1931 UNITED STATES PATENT OFFICE I WILLIS R. WHITNEY,OF NISKAYUNA, NEW YORK, ASSIGNQR TO GENERAL ELECTRIC COMPANY, ACORPORATION F NEW YORK PHOTO-ELECTRIC SYSTEM Application Ied June 19,1925.

Mypresent invention relates to light sensitive apparatus such asphoto-electric cells, and more particularly to the use of such cells asa means for comparing the light conductivity of a fixed or known lightfilter with a variable light filter, such as paper pulp, or any turbidor colored solution.

In the use of photo-electric cells as a means for comparing lightintensities, it has been 3e dit'icult to procure a substantiallyconstant potential for both circuits of the cell, i. e. a steadypotential for the source of light employed and a steady potential forthe cell it self. As a consequence of my invention, an le easilyavailable electric source, such as a lighting or power circuit, can beused for operating photo-electric apparatus, without introducing errorsin the photo-electric currents due to the unavoidable variations involtage 2o of such a circuit.

ln the present instance, instead ot using a sin gle photo-electric cellI have employed two such cells having a common source of energy tosupply the potential across the cells. By using two cells in this mannerl employ but one source of light which may or may not be connected incircuit with the common source of supply for the two cells. One cellreceives light from the light source after passing through a fixed orknown filter, while the other receives light through the filter which isthe substance to be measured. The cells are so connected thatthe'currents produced in them by the action of light, oppose each other,and

any difference in the currents produced by the two cells is indicated ona galvanometer or other suitable device. Since a single lamp is used toilluminate both cells any slight change in voltage across the lamp doesnot 4@ produce any serious defect as both cells are equally affected byany change in the intensity of the light source. y

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims.`

My invention itself, however, both as to its organization and method ofoperation will best be understood byy reference to the followingdescription taken in connection with 5 the accompanying drawing in whichFig. 1

Serial No. 38,377.

shows a circuit organization whereby my inventlon may be carried intoeect, the invention in the instance shown being applied to means formaintaining paper pulp at a substantially constant density. Fig. 2 showsa modilied motor control system.

Referring to the drawing I have indicated at 1 a pulp tank having awater supply pipe line 2 and a. pulp supply pipe line 3. The pulp fromthe tank l may be supplied directly to a paper machine through a pipeline 4l or, if desired, the line a may simply constitute means whereby asample of the pulp may be obtainedV in which latter case pipe lineewould be returned to the tank 1.

In the supply pipe l l have inserted a motor driven pump 5 and atransparent window portion 6. ln order to maintain the density of thepulp supply to the paper machine substantially constant, l associatewith the window portion 6 of the supply pipe 4.., means to control theaction of a valve connected with the water supply line 2. The meansemployed includes a TWheatstone bridge having variable resistors 8 and 9respectively in two arms of the bridge, while the other two arms includeresistors which in the present instance constitute photoelec tric cells10 and 11. The bridge is supplied from a source of energy 12, and anyvariation in current in the arms of the bridge is indicated by the usualgalvanometer 13.

A common source of light 14, which may be energized from any suitablesource of power 15 cooperates with both photo-electric cells. A knowniilter or light controlling means 16, which may be of paper or anysuitable material, is placed between the source 14 and cell 10, whilethe transparent portion 6 of the supply line l is placed between thesource 14 and the cell 11. The cells are connected so that the currentsproduced in them oppose each other. The resistors 8 and 9 are thenadjusted so that when the pulp is -of the desired density, no currentwill flow through galvanometer 13.

In the operation of the device, when there is any variation/ini thephysical or optical as color, opacity or pulp density, thecurcharacteristicsyof the pulp such for example l rent roduced by cell11 will vary proportionally to the variations in the physicalcharacteristics of the pulp and the needle of galvanometer 13 will moveto the right or left of the zero or normal position and close a circuitfrom a source of energy 17 through relay 18 or 19 depending on thenature of the change in the pulp solution. Relays 18 and 19 control theenergization of coils 20 and 21 which operate reversing switches 22 and23 respectively. When one of the reversing switches` 23 for instance, 1soperated, current is supplied from mains 24 to motor 25 to further openvalve 7 and increase the supply of: water to the pulp tank 1 to therebyreduce the density of the pulp solution. Operation of switch 22 suppliescurrent in the opposite direction to the armature of motor 25 causingreverse operation of the motor to close the valve 7 and thereby decreasethe supply of water to the tank 1. A winding 26 is connected across thearmature of motor 25. The Winding controls the operation of a switch 27which governs a dynamic braking resistor 28. Deenergization of'switches22 and 23 enables switch 27 Y to close and complete a dynamic brakingciry32 if desired.

cuit for motor 25 through the braking resistor 28 and thereby promptlystop the motor. Pump 5'may be mechanically connected wlth a drivingmotor 29 in any manner desired. Instead of the direct current motor 29,an'y substantially constant speed driving device may be employed.

In Fig. 2 I have shown a modified form of motor control for the valvemotor 25. In this figure galvanometer 11 controls relays r18 and 19 asin Fig. 1. rIhe relays control 'resistors 30 and 31 respectively in theshunt field circuit of motor 25, one of the resistors 30 being normallyshort circuitcd by relay 18.

In the operation of the device as shown in Fig. 2 when the galvanometerneedle moves to the left, relay 18 is energized to insert resistor 30 inthe shunt field circuit to thereby increase the speed of motor 25.Likewise, energization of relay 19 short circuits resistor 31 todecrease the speed of motor 25. Each of switches 18 and 19 maybe'maintained in normal position by means of springs Although I'haveillustrated myV invention as applied to paper making it is obviously notrestricted to use in that art alone. While I have shown the motor 25controlling the supply of the water to the pulp tank obvi-y ously thewater supply might be maintained constant and a valve in the pulp supplyline 3 be controlled by motor 24 to vary lthe amount 'of pulp suppliedto tank 1. It is alsol obvious that the arrangement shown can be usedfor reflected, instead of transmitted light, so that opaque surfaces canbe quantitatively compared or controlled as to theiry reecting powers orcolors. Various modifications of my invention will readily suggestthemselves to persons skilled in the art without departing from thescope of my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. In combination, a plurality of photoelectric cells, said cells beingso connected that the currents produced by them are in opposition, asource of energy, connections between said source of energy and saidcells, a single source of light cooperating with said cells, independentmeans interposed between each of said cells and said source of light forcontrolling the amount of light delivered to the cells, andelectro-responsive means operated by the difference in current in saidcells.

2. Means for determining the light reflected from or transmitted by a`given medium, said means comprising a circuit including a plurality ofphoto-electric cells, said cells being so connected that the currentsproduced by them are in opposition, a single source of light adapted tocontrol the operation of said cells, independent light controllingmediums interposed between said source of light and each of said cells,and electroresponsive means operated by the difference in current insaid two cells.

3. In a device of the class described, a Wheatstone bridge, a source ofenergy eonnected to said bridge, a light sensitive cell in each of twoarms of the bridge, a source of light adapted to control the operationof said cells, a fixed or known light filter interposed between saidsource and one of said cells, a variable light ilter interposed betweenthe source and said other photo-electric cell, and

electro-responsive means operated by the difference in current in saidtwo cells.

4. In a device of the class described, a Wheatstone bridge, a source ofenergy connected to the bridge, a light sensitive cell in each of twoarms of said bridge, said cells being connected so that the currentsproduced by them are in opposition, a source of light cooperating witheach of said cells, the light directed onto one cell being substantiallyconstant, a light controlling means .interposed between the other ofsaid cells and said source `of light, and an electro-responsive meansassociated with said bridge and operated by v variations in the physicalcharacteristics of tween its associated cell and said source of light,and electromagnetic means associated .with said bridge and responsive tovariations in the currents in said cells.

i 6. Means for indicating variations in the density of paper pulpsupplied to a paper making machine, said means comprising a Wheatstonebridge, a source of ener `con- A nected to said bridge, a lightsensitlve cell connected in each of two arms of said bridge, a source ofli ht cooperating with each of said cells, the 'ght directed onto onecell being substantially constant, means for passin light from saidsource to the other of sai 1; cells through'a portion of the pulpsupplied to said machine, whereby changes in pulp density produceproportional changes in the current produced by the latter cell, andvmeans for indicating variations in the current produced in said latterce 7. In combination, a Wheatstone bridge, a.

, source of energy connected to the bridge, a light-sensitive cell inone of the arms of said bridge, a source of light cooperating'l withlsaid cell, a light'controlling means inter osed between said source oflight and said ce and means comprising an electro-responsive device forindicating variations in the physical characteristics 'of said li ht`controlling ao means and for controlling sai light controlling means. v

8. Apparatus responsive to an 4optical characteristic of a medium, saidapparatus Ycomprising a Wheatstone bridge, a lightsensitive cellelectrically connected in one of the arms of said bridge, alight-sensitivelcell electrically connected in another arm of saidbridge, and means for va g the resistance of one of said cells inaccorldilce with changes 40 in the optical characteristics of saidmedium while maintaining the resistance of the other cell substantiallyconstant.

In witness whereof, I have hereunto set my hand this 17th day of June,1925. WILLIS R. WHITNEY.

